Apparatus and method for recovery of synchronization in wireless communication system

ABSTRACT

The present disclosure relates to a pre-5 th -Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4 th -Generation (4G) communication system such as Long Term Evolution (LTE). According to various embodiments of the disclosure, an apparatus of a terminal in a wireless communication system is provided. The apparatus includes at least one transceiver, and at least one processor configured to be operatively connected to the at least one transceiver, wherein the at least one processor may be configured to: obtain first synchronization of a first carrier that is in synchronization, determine second synchronization of a second carrier that is out of synchronization based on the first synchronization, and perform communication based on the second synchronization.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(a) of a Korean patent application number 10-2018-0026971, filed onMar. 7, 2018, in the Korean Intellectual Property Office, the disclosureof which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to a wireless communication system. Moreparticularly, the disclosure relates to an apparatus and a method forrecovering synchronization in a wireless communication system.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4th generation (4G) communication systems, efforts havebeen made to develop an improved 5th generation (5G) or pre-5Gcommunication system. Therefore, the 5G or pre-5G communication systemis also called a ‘Beyond 4G Network’ or a ‘post long term evolution(LTE) system’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 28 GHz or 60 GHz bands, so as toaccomplish higher data rates. To decrease propagation loss of the radiowaves and increase the transmission distance, the beamforming, massivemultiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO),array antenna, an analog beam forming, large scale antenna techniquesare discussed in 5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud radioaccess networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, coordinated multi-points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, hybrid frequency shift keying (FSK) and quadratureamplitude modulation (FQAM) and sliding window superposition coding(SWSC) as an advanced coding modulation (ACM), and filter bank multicarrier (FBMC), non-orthogonal multiple access (NOMA), and sparse codemultiple access (SCMA) as an advanced access technology have beendeveloped.

To receive signals on resources in a wireless communication system, theterminal is required to acquire synchronization. If the terminal failsto acquire the synchronization successfully, it may be difficult for theterminal to receive the signals successfully.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure provides anapparatus and a method for successful synchronization in a wirelesscommunication system.

Another aspect of the disclosure is to provide an apparatus and a methodfor recovering synchronization when synchronization fails in a wirelesscommunication system.

Another aspect of the disclosure is to provide an apparatus and a methodfor recovering the synchronization of a component carrier (CC), which isout of synchronization, using the synchronization of a CC, which is insynchronization, in carrier aggregation (CA) of a wireless communicationsystem.

Another aspect of the disclosure is to provide an apparatus and a methodfor recovering synchronization without going through radio link failure(RLF) or radio re-establishment (RRE) in a wireless communicationsystem.

Another aspect of the disclosure is to provide an apparatus and a methodfor recovering synchronization through inter-frequency measurement.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

In accordance with an aspect of the disclosure, an apparatus of aterminal in a wireless communication system is provided. The apparatusincludes at least one transceiver, and at least one processor configuredto be operatively connected to the at least one transceiver, wherein theat least one processor may be configured to obtain a firstsynchronization of a first carrier that is in synchronization, determinea second synchronization of a second carrier that is out ofsynchronization based on the first synchronization, and performcommunication based on the second synchronization.

In accordance with another aspect of the disclosure, an operating methodof a terminal in a wireless communication system is provided. Theoperation method includes obtaining a first synchronization of a firstcarrier that is in synchronization, determining a second synchronizationof a second carrier that is out of synchronization based on the firstsynchronization, and performing communication based on the secondsynchronization.

The apparatus and method according to various embodiments of thedisclosure can quickly recover synchronization, thereby efficientlyperforming wireless communication.

Effects which can be acquired by the disclosure are not limited to theabove described effects, and other effects that have not been mentionedmay be clearly understood by those skilled in the art from the followingdescription.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates a wireless communication system according to anembodiment of the disclosure;

FIG. 2 illustrates a configuration of a base station in a wirelesscommunication system according to an embodiment of the disclosure;

FIG. 3 illustrates a configuration of a terminal in a wirelesscommunication system according to an embodiment of the disclosure;

FIG. 4A illustrates a configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure;

FIG. 4B illustrates a configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure;

FIG. 4C illustrates a configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure;

FIG. 5 illustrates an example of synchronization compensation accordingto an embodiment of the disclosure;

FIG. 6 illustrates a flowchart of a terminal for synchronizationcompensation according to an embodiment of the disclosure;

FIG. 7 illustrates a flowchart of a terminal for determining a successor failure of synchronization in carrier aggregation (CA) according toan embodiment of the disclosure;

FIG. 8A illustrates a flowchart of a terminal for determining thesuccess or failure of synchronization for each carrier according to anembodiment of the disclosure;

FIG. 8B illustrates a flowchart of a terminal for early synchronizationcompensation according to an embodiment of the disclosure;

FIG. 9 illustrates a flowchart of a terminal for synchronizationcompensation according to an embodiment of the disclosure;

FIG. 10 illustrates an example of a timer of a terminal forsynchronization compensation according to an embodiment of thedisclosure;

FIG. 11A illustrates an example of synchronization compensation based oncell-deployment according to an embodiment of the disclosure;

FIG. 11B illustrates an example of synchronization compensation based onan RF path according to an embodiment of the disclosure;

FIG. 12 illustrates a flowchart of a terminal for determining thesuccess or failure of CA synchronization according to an embodiment ofthe disclosure; and

FIG. 13 illustrates a flowchart of a terminal for signal processingaccording to the success or failure of CA synchronization according toan embodiment of the disclosure.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

Hereinafter, various embodiments of the disclosure will be describedbased on an approach of hardware. However, various embodiments of thedisclosure include a technology that uses both hardware and software andthus, the various embodiments of the disclosure may not exclude theperspective of software.

Hereinafter, the disclosure relates to an apparatus and a method forrecovering synchronization in a wireless communication system.Specifically, the disclosure describes a technique for recoveringsynchronization of a cell, which is out of synchronization, based on thesynchronization of a cell, which is in synchronization, in a wirelesscommunication system.

Terms {e.g., “carrier”, “cell”, “band”, “carrier frequency”, “band”,“component carrier (CC)”, etc.} referring to frequency, terms referringto network entities, terms referring to components of an apparatus, andthe like, which are used hereinafter, are illustrative words for theconvenience of explanation. Accordingly, the disclosure is not limitedto the terms described below, and other terms having equivalenttechnical meanings may be used.

In addition, the disclosure will describe various embodiments usingterms used in some communication standards {e.g., 3^(rd) generationpartnership project (3GPP)}, but this is merely an illustrative example.The various embodiments of the disclosure may be easily modified andapplied to other communication systems as well.

FIG. 1 illustrates a wireless communication system according to anembodiment of the disclosure.

Referring to FIG. 1 illustrates a base station 110, a terminal 120, anda terminal 130 as parts of nodes using wireless channels in a wirelesscommunication system.

The base station 110 is a network infrastructure element that provideswireless access to the terminals 120 and 130. The base station 110 has acoverage defined as a certain geographic area based on the distance overwhich signals can be transmitted. The base station 110 may be referredto as an “access point (AP)”, an “eNodeB (eNB)”, a “5^(th) generation(5G) node”, a “wireless point”, or other terms having equivalenttechnical meanings, as well as a base station. According to variousembodiments, the base station 110 may be connected to one or more“transmission/reception points (TRPs)”. The base station 110 maytransmit downlink signals to the terminal 120 or 130 or receive uplinksignals from the terminal 120 or 130 via one or more TRPs.

The terminals 120 and 130 are devices used by a user and communicatewith the base station 110 via wireless channels. In some cases, at leastone of the terminals 120 and 130 may be operated without userinvolvement. That is, at least one of the terminals 120 and 130 may be adevice for performing machine type communication (MTC), and may not becarried by a user. Each of the terminals 120 and 130 may be referred toas “user equipment (UE)”, a “mobile station”, a “subscriber station”,“customer premises equipment (CPE)”, a “remote terminal”, a “wirelessterminal”, an “electronic device”, a “user device”, or other termshaving equivalent technical meanings, as well as a terminal.

The base station 110, the terminal 120, and the terminal 130 maytransmit and receive radio signals in a millimeter wave (mmWave) band(e.g., 28 GHz, 30 GHz, 38 GHz, or 60 GHz). In this case, in order toimprove the channel gain, the base station 110, the terminal 120, andthe terminal 130 may perform beamforming. The beamforming may includetransmission beamforming and reception beamforming. That is, the basestation 110, the terminal 120, and the terminal 130 may assigndirectivity to a transmission signal or a reception signal. To this end,the base station 110 and the terminals 120 and 130 may select servingbeams 112, 113, 121, and 131 through a beam search or beam managementprocedure. After the serving beams 112, 113, 121, and 131 are selected,subsequent communication may be performed via resources that are in aquasi-co-located (QCL) relationship with the resources that transmittedthe serving beams 112, 113, 121, and 131.

If the large-scale characteristics of the channel that carried thesymbol on the first antenna port can be inferred from the channel thatcarried the symbol on the second antenna port, it can be determined thatthe first antenna port and the second antenna port are in a QCLrelationship. For example, the large-scale characteristics may includeat least one of delay spread, Doppler spread, Doppler shift, an averagegain, average delay, and spatial receiver parameters.

Hereinafter, a cell may correspond to a carrier frequency in thedisclosure. A plurality of cells can be classified according to thesupported frequency and the area of a covering sector. In addition, thecell may indicate the area that can be covered by a single base station.One base station may cover one cell, or may cover multiple cells. “Basestation” may be used as a term encompassing the cell, or “cell” may beused as a term referring to the base station.

FIG. 2 illustrates a configuration of a base station in a wirelesscommunication system according to an embodiment of the disclosure. Theconfiguration illustrated in FIG. 2 may be regarded as the configurationof the base station 110. Hereinafter, the term “-unit”, “-or (er)”, orthe like denotes a unit for processing at least one function oroperation, and may be implemented as hardware, software, or acombination thereof.

Referring to FIG. 2, the base station 110 includes a wirelesscommunication unit 210, a backhaul communication unit 220, a storageunit 230, and a controller 240.

The wireless communication unit 210 may perform functions oftransmitting and receiving signals via a wireless channel. For example,the wireless communication unit 210 may perform a function oftransformation between a baseband signal and a bit stream according tothe physical layer standard of a system. For example, in the case ofdata transmission, the wireless communication unit 210 may generatecomplex symbols by encoding and modulating a transmission bit stream. Inthe case of data reception, the wireless communication unit 210 mayrestore a reception bit stream by demodulating and decoding a basebandsignal. In addition, the wireless communication unit 210 may up-converta baseband signal to a radio frequency (RF) band signal to thus transmitthe same via an antenna, and may down-convert an RF band signal receivedvia the antenna to a baseband signal.

To this end, the wireless communication unit 210 may include atransmitting filter, a receiving filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. In addition, the wireless communicationunit 210 may include a plurality of transmission/reception paths.Further, the wireless communication unit 210 may include at least oneantenna array including a plurality of antenna elements. In terms ofhardware, the wireless communication unit 210 may include a digital unitand an analog unit, and the analog unit may include a plurality ofsub-units depending on the operation power, operation frequency, and thelike.

The wireless communication unit 210 may transmit and receive signals.For example, the wireless communication unit 210 may transmit asynchronization signal, a reference signal, system information,messages, control information, data, and the like. The wirelesscommunication unit 210 may also perform beamforming. The wirelesscommunication unit 210 may apply a beamforming weight to a signal inorder to assign directivity to a signal to be transmitted/receivedaccording to the setting of the controller 240.

The wireless communication unit 210 transmits and receives signals asdescribed above. Accordingly, all or some of the wireless communicationunit 210 may be referred to as a “transmitter”, a “receiver”, or a“transceiver”. In the following description, the transmission andreception performed via a wireless channel will be used as a meaning toencompass the execution of the process by the wireless communicationunit 210 as described above.

The backhaul communication unit 220 provides an interface forcommunication with other nodes in the network. That is, the backhaulcommunication unit 220 converts a bit stream, transmitted from the basestation 110 to another node, such as another access node, another basestation, an upper node, or a core network, into a physical signal andconverts a physical signal received from another node into a bit stream.

The storage unit 230 stores data such as fundamental programs,application programs, and configuration information for the operation ofthe base station 110. The storage unit 230 may be configured as avolatile memory, a non-volatile memory, or a combination thereof. Inaddition, the storage unit 230 provides the stored data upon request bythe controller 240.

The controller 240 controls the overall operation of the base station110. For example, the controller 240 transmits and receives signals viathe wireless communication unit 210 or the backhaul communication unit220. The controller 240 writes or reads data to or from the storage unit230. In addition, the controller 240 may perform the functions of aprotocol stack required for the communication standard. To this end, thecontroller 240 may include at least one processor. According to variousembodiments, the controller 240 may perform control such that the basestation 110 performs operations, which will be described later,according to various embodiments.

FIG. 3 illustrates the configuration of a terminal in a wirelesscommunication system according to an embodiment of the disclosure. Theconfiguration illustrated in FIG. 3 may be regarded as the configurationof the terminal 120. Hereinafter, the term “-unit”, “-or (er)”, or thelike denotes a unit for processing at least one function or operation,and may be implemented by hardware, software, or a combination thereof.

Referring to FIG. 3, the terminal 120 includes a communication unit 310,a storage unit 320, and a controller 330.

The communication unit 310 performs functions of transmitting andreceiving signals via a wireless channel. For example, the communicationunit 310 may perform a function of transformation between a basebandsignal and a bit stream according to the physical layer standard of asystem. For example, in the case of data transmission, the communicationunit 310 may generate complex symbols by encoding and modulating atransmission bit stream. In the case of data reception, thecommunication unit 310 may restore a reception bit stream bydemodulating and decoding a baseband signal. In addition, thecommunication unit 310 may up-convert a baseband signal to an RF bandsignal to thus transmit the same via an antenna, and may down-convert anRF band signal received via the antenna to a baseband signal. Forexample, the communication unit 310 may include a transmitting filter, areceiving filter, an amplifier, a mixer, an oscillator, a DAC, an ADC,and the like.

In addition, the communication unit 310 may include a plurality oftransmission/reception paths. Further, the communication unit 310 mayinclude at least one antenna array including a plurality of antennaelements. In terms of hardware, the communication unit 310 may include adigital circuit and an analog circuit {e.g., radio frequency integratedcircuit (RFIC)}. The digital circuit and the analog circuit may beimplemented as a single package. In addition, the communication unit 310may include a plurality of RF chains. The communication unit 310 mayperform beamforming. The communication unit 310 may apply a beamformingweight to a signal in order to assign directivity to a signal to betransmitted/received according to the setting of the controller 330.

In addition, the communication unit 310 may transmit and receivesignals. For example, the communication unit 310 may receive asynchronization signal, a reference signal, system information,messages, control information, data, and the like.

In addition, the communication unit 310 may include differentcommunication modules to process signals in different frequency bandsfrom each other. Furthermore, the communication unit 310 may include aplurality of communication modules to support a plurality of differentwireless access technologies. For example, the different wireless accesstechnologies may include Bluetooth low energy (BLE), Wi-Fi, Wi-Figigabyte (WiGig), cellular networks {e.g., long term evolution (LTE) ornew radio (NR)}, and the like. In addition, different frequency bandsmay include a super-high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) bandand a millimeter wave (e.g., 38 GHz or 60 GHz) band.

The communication unit 310 transmits and receives signals as describedabove. Accordingly, all or some of the communication unit 310 may bereferred to as a “transmitter”, a “receiver”, or a “transceiver”. In thefollowing description, the transmission and reception performed via awireless channel will be used as a meaning to encompass the execution ofthe process by the communication unit 310 as described above.

The storage unit 320 may store data such as fundamental programs for theoperation of the terminal 120, application programs, and data such asconfiguration information. The storage unit 320 may be configured as avolatile memory, a non-volatile memory, or a combination thereof. Inaddition, the storage unit 320 provides the stored data upon request bythe controller 330. According to various embodiments, the storage unit320 may store synchronization information. The synchronizationinformation may include a carrier frequency (i.e., synchronizationinformation on each CC). In addition, according to various embodiments,the storage unit 320 may store beam information. The beam informationmay relate to a CC. According to an embodiment, the beam information mayinclude a group of beams. According to various embodiments, the storageunit 320 may include information {e.g., timing advance (TA) information)related to the physical location of the cell. According to variousembodiments, the storage unit 320 may include statistical information(e.g., the amount of synchronization variation) related to thesynchronization.

The controller 330 controls the overall operation of the terminal 120.For example, the controller 330 transmits and receives signals via thecommunication unit 310. The controller 330 writes or reads data to orfrom the storage unit 320. The controller 330 may perform the functionsof a protocol stack required for the communication standard. To thisend, the controller 330 may include at least one processor ormicro-processor, or may be a part of a processor. In addition, a part ofthe communication unit 310 and the controller 330 may be referred to asa “CP”. The controller 330 may include various modules for performingcommunication.

According to various embodiments, the controller 330 may include asynchronization obtainer 331 for obtaining synchronization from thesignal of a cell, a synchronization success determiner 333 fordetermining whether or not the cell is in synchronization or out ofsynchronization depending on whether or not the synchronization of thecell satisfies a predetermined condition, a synchronization recoverer335 for recovering the synchronization of a cell and determining thesuccess or failure of synchronization of the cell according to thesynchronization recovery procedure of the disclosure, and asynchronization information manager 337 for controlling synchronizationinformation for each cell or each beam. The synchronization obtainer331, the synchronization success determiner 333, the synchronizationrecoverer 335, and the synchronization information manager 337, whichare a set of instructions or codes stored in the storage unit 320, maybe instructions/codes residing at least temporarily in the controller330, a storage space storing the instructions/codes, a part of thecircuitry constituting the controller 330, or a module for performingthe function of the controller 330. According to various embodiments,the controller 330 may perform control such that the terminal performsthe operations according to various embodiments described below.

Although it is not shown in FIG. 3, in some embodiments, the terminalmay further include separate hardware such as a free running counter(FRC). The FRC is a component that provides a reference value forindicating the cell time. The terminal may use the FRC and a cell timerfor each carrier, thereby determining the success or failure ofsynchronization for each carrier and compensating for synchronization ofa specific cell based on the synchronization of another cell. In thiscase, the FRC may be connected to the respective cell timers to thusprovide a reference value. In some embodiments, the apparatus furthercomprises a free running counter (FRC), the FRC configured to provide areference value indicating cell time.

The configuration of the terminal shown in FIG. 3 is only an example ofa terminal, and the terminal is not limited thereto. That is, someconfigurations may be added, excluded, or modified according to variousembodiments. For example, the synchronization success determiner 333 ofthe controller 330 may be implemented as an independent configurationfor each cell configured for the CA. For example, the above-describedFRC may be functionally implemented as a component of the controller330.

FIG. 4A illustrates the configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure.

FIG. 4B illustrates the configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure.

FIG. 4C illustrates the configuration of a communication unit in awireless communication system according to an embodiment of thedisclosure. FIGS. 4A to 4C show examples of the detailed configurationof the wireless communication unit 210 in FIG. 2 or the communicationunit 310 in FIG. 3. More specifically, FIGS. 4A to 4C illustratecomponents for performing beamforming as parts of the wirelesscommunication unit 210 in FIG. 2 or the communication unit 310 in FIG.3.

Referring to FIG. 4A, the wireless communication unit 210 or thecommunication unit 310 includes an encoder/modulator 402, a digitalbeamforming unit 404, a plurality of transmission paths 406-1 to 406-N,and an analog beamforming unit 408.

The encoder/modulator 402 performs channel encoding. At least one oflow-density parity check (LDPC) code, convolution code, and polar codemay be used for the channel encoding. The encoder/modulator 402generates modulation symbols by performing constellation mapping.

The digital beamforming unit 404 performs beamforming for digitalsignals (e.g., modulation symbols). To this end, the digital beamformingunit 404 multiplies the modulation symbols by beamforming weights. Thebeamforming weights may be used to change the magnitude and phase of thesignal, and may be referred to as a “precoding matrix”, a “precoder”, orthe like. The digital beamforming unit 404 outputs digital-beamformedmodulation symbols to a plurality of transmission paths 406-1 through406-N. In this case, according to a multiple-input multiple-output(MIMO) transmission scheme, the modulation symbols may be multiplexed,or the same modulation symbol may be provided to the plurality oftransmission paths 406-1 through 406-N.

The plurality of transmission paths 406-1 through 406-N convert thedigital signals, which are digitally beamformed, into analog signals. Tothis end, each of the plurality of transmission paths 406-1 to 406-N mayinclude an inverse fast Fourier transform (IFFT) operator, a cyclicprefix (CP) inserter, a DAC, and an up-converter. The CP inserter isintended for an orthogonal frequency division multiplexing (OFDM)scheme, and may be excluded in the case where other physical layerschemes {e.g., filter bank multi-carrier (FBMC)} are applied. That is,the plurality of transmission paths 406-1 through 406-N provideindependent signal processing procedures for the plurality of streamsgenerated through digital beamforming. However, depending on theimplementation, some of the components of the plurality of transmissionpaths 406-1 through 406-N may be used in common.

The analog beamforming unit 408 performs beamforming on the analogsignals. To this end, the digital beamforming unit 404 multiplies theanalog signals by beamforming weights. The beamforming weights are usedto change the magnitude and phase of the signals. More specifically, theanalog beamforming unit 408 may be configured as shown in FIG. 4B or 4Cdepending on the connection structures between the plurality oftransmission paths 406-1 to 406-N and the antennas.

Referring to FIG. 4B, signals input to the analog beamforming unit 408are processed with operations of phase/magnitude conversion andamplification and then transmitted through the antennas. At this time,the signals of the respective paths are transmitted through differentsets of antennas (i.e., antenna arrays). As to the processing of asignal input through a first path, the signal is converted into signalstreams having the same or different phases/magnitudes by thephase/magnitude converters 412-1-1 to 412-1-M, amplified by theamplifiers 414-1-1 to 414-1-M, and then transmitted through theantennas.

Referring to FIG. 4C, signals input to the analog beamforming unit 408are processed with operations of phase/magnitude conversion andamplification and then transmitted through the antennas. At this time,the signals of the respective paths are transmitted through the same setof antennas (i.e., antenna array). As to the processing of a signalinput through a first path, the signal is converted into signal streamshaving the same or different phases/magnitudes by the phase/magnitudeconverters 412-1-1 to 412-1-M and amplified by the amplifiers 414-1-1 to414-1-M. In addition, the amplified signals are summed by the adders416-1-1 to 416-1-M so as to be transmitted through one antenna arraybased on the antenna elements, and are then transmitted through theantennas.

FIG. 4B shows an example in which an independent antenna array is usedfor each transmission path, and FIG. 4C shows an example in whichtransmission paths share one antenna array. However, according toanother embodiment, some transmission paths may use independent antennaarrays, and the remaining transmission paths may share one antennaarray. According to another embodiment, a structure that adaptivelychanges depending on the situation may be used by applying a switchablestructure between the transmission paths and the antenna arrays.

In next generation communication system standards, such as pre-5G or newradio (NR), operation of a shorter transmission time interval (TTI) isunder consideration. As the TTI becomes shorter, the length of thecyclic prefix (CP) in the symbol, as well as the symbol, becomesshorter, which may increase the failure of synchronization. In addition,since the influence of frequency selectivity is increased due to theincrease in the transmission bandwidth, the synchronization may bebroken between the carrier frequencies. Furthermore, since beamformingdue to transmission in a high-frequency band is supported,synchronization further varies depending on the physical location of thebase station providing the cell.

Therefore, it is required to control synchronization more strictly infuture communication systems. If radio link failure (RLF) is declaredand time synchronization is recovered through RRE {radio resourcecontrol (RRC) connection re-establishment} for every synchronizationfailure, data transmission/reception is interrupted during the executionof the RRE, so that the user experiences deterioration in communicationquality such as interruption of a streaming service or degradation ofthe quality of service (QoS). In addition, since additional procedures,such as a procedure for searching for a new beam (e.g., beam search orbeam sweeping), are required in standards supporting beamforming, thecommunication quality may be further degraded.

Thus, hereinafter, a method for recovering synchronization of a cellthat is out of synchronization, even when the cell is out ofsynchronization, based on the synchronization of a cell that is insynchronization, instead of immediately performing a reconnectionprocedure, such as RRE, will be described. Now, a method for recoveringsynchronization will be described with reference to FIG. 5.

FIG. 5 illustrates an example of synchronization recovery according toan embodiment of the disclosure. The terminal may perform carrieraggregation (CA) including a plurality of component carriers (CCs). TheCC is a frequency unit of serving cells constituting the CA, and may bereferred to as a “carrier frequency”, a “carrier frequency band”, a“carrier”, or the like. Hereinafter, the CC will be referred to as a“carrier” for description.

Referring to FIG. 5, the terminal may perform the CA through fourcarriers (a first carrier 511, a second carrier 512, a third carrier513, and a fourth carrier 514). The terminal may transmit or receivedata through four carriers. The terminal is required to successfullyobtain synchronization for each of the four carriers in order to operatethe four carriers.

The terminal may receive a synchronization signal. For example, theterminal may receive a physical synchronization signal (PSS) from a basestation. The terminal may obtain the cell time of the cell based on thesynchronization signal. The cell time refers to the synchronization ofthe carrier. That is, determining the synchronization of the carriermeans determining the cell time of the cell providing the correspondingcarrier. The terminal may determine the success or failure ofsynchronization of a carrier from the cell time. Hereinafter, an examplein which the synchronization for the second carrier 512 and the fourthcarrier 514, which is performed by the terminal, succeeded, but thesynchronization for the first carrier 511 and the third carrier 513failed will be described. In the disclosure, “success ofsynchronization” means that the carrier becomes synchronized {thesituation in which an error between each resource boundary (e.g., symbolboundary) of the base station and the resource boundary of the terminalis within a predetermined range}, and “failure of synchronization” meansthat the carrier becomes out of synchronization {the situation in whichan error between each resource boundary (e.g., symbol boundary) of thebase station and the resource boundary of the terminal is out of apredetermined range}.

The terminal is required to recover synchronization of the cells thatare out of synchronization. If the terminal does not recover thesynchronization of a cell that is out of synchronization, the terminalwill continuously decode signals at the erroneously obtained cell time,so that the terminal cannot properly receive control information ordata, and additionally wastes power. In addition, if reconnection, suchas an RRE procedure or deletion/addition of the Scell is performed inorder to re-obtain synchronization, data interruption occurs, therebycausing degradation of communication quality.

The terminal according to various embodiments may obtain synchronizationof carriers (e.g., the first carrier 511 and the third carrier 513) of acell that is out of synchronization based on the synchronization ofcarriers (e.g., the second carrier 512 and the fourth carrier 514) of acell that is in synchronization. The procedure of obtaining thesynchronization of the carrier of a cell that is out of synchronizationbased on the synchronization of the carrier of a cell that is insynchronization will be referred to as “synchronization compensation” inthe disclosure. For example, the terminal may obtain the compensatedsynchronization 521 of the first carrier 511 through the synchronizationcompensation based on the synchronization of the second carrier 512. Inaddition, the terminal may obtain the compensated synchronization 523 ofthe third carrier 513 through synchronization compensation based on thesynchronization of the fourth carrier 514.

The terminal may determine whether or not the synchronization of eachcarrier is successful after the synchronization compensation. Theterminal may determine whether or not the synchronization of thecarrier, which is out of synchronization, is recovered (hereinafter,referred to as “synchronization recovery”). That is, the terminal maydetermine whether or not the synchronization of the carrier, which isout of synchronization, is recovered based on the synchronization of thecarrier that is out of synchronization, which is obtained through thesynchronization compensation. In other words, the terminal may determinewhether or not the carrier, which was out of synchronization at first,becomes synchronized through the synchronization compensation. Forexample, the terminal may determine the success of synchronization ofthe first carrier 511 through the compensated synchronization 521. Inaddition, the terminal may determine the success of synchronization ofthe third carrier 513 through the compensated synchronization 523.

If all the carriers configured for the CA becomes synchronized, theterminal may transmit or receive data via the CA. Although it is notshown in FIG. 5, if synchronization of some carriers is not recovered,the terminal may perform the RRE or perform the Scell deletion/addition.

As described with reference to FIG. 5, the terminal may recoversynchronization of a carrier through the synchronization compensation.When the CA is set, the terminal may perform synchronizationcompensation independently for each carrier. Although FIG. 5 has beendescribed based on the CA, the disclosure is not limited thereto. Thedisclosure can be applied to any communication procedure for performingsynchronization compensation to determine the synchronization of acarrier based on synchronization of another carrier. For example, in thecase where a specific carrier is out of synchronization, the terminalmay determine the synchronization of the specific carrier based onsynchronization information of another carrier, which is obtainedthrough inter-frequency measurement. Hereinafter, the operations of theterminal for synchronization compensation or synchronization recoverywill be described with reference to FIGS. 6 and 7.

FIG. 6 illustrates a flowchart of a terminal for synchronizationrecovery according to an embodiment of the disclosure. The terminal maybe the terminal 120 in FIG. 1.

Referring to FIG. 6, the terminal may obtain the first synchronizationof a first carrier that is in synchronization in operation 601. Theterminal may identify the first carrier in synchronization. The terminalmay determine the success or failure of synchronization of each carrierin order to identify the first carrier in synchronization.

The terminal may determine whether or not respective carriers are insynchronization. The terminal may determine whether respective cells arein synchronization or out of synchronization. The terminal may obtainsynchronization of each of a plurality of carriers for the terminal, andmay determine the success or failure of synchronization of each cellaccording to the obtained synchronization. The synchronizationacquisition and the determination on the success or failure ofsynchronization may be independently performed for each carrier.

The terminal may determine the success or failure of synchronization ofa carrier. For example, the terminal may determine the success orfailure of synchronization of the corresponding cell based on whether ornot a synchronization signal correlation value is detected during thetime corresponding to the synchronization. In addition, the terminal maydetermine the success or failure of synchronization of the correspondingcell according to, for example, whether or not the time corresponding tothe synchronization is within a predetermined range. In addition, theterminal may determine the success or failure of synchronization of thecorresponding cell based on, for example, the channel quality.

At least one carrier that is in synchronization, among a plurality ofcarriers, may include the first carrier. The terminal may obtain thefirst synchronization of the first carrier. The acquisition of the firstsynchronization means that the cell time of the first cell isdetermined. The cell time means the time at which a signal (e.g., asynchronization signal) of the cell is transmitted within an absolutetime period (e.g., 10 ms). The terminal may determine the cell time ofthe first cell from the synchronization signal transmitted through thefirst cell. For example, the terminal may receive the PSS transmittedthrough the first cell twice, thereby determining the cell time of thefirst cell. The first synchronization may be the cell time of the firstcell, which is obtained when the success or failure of thesynchronization is determined.

In operation 603, the terminal may determine the second synchronizationof the second carrier that is out of synchronization based on the firstsynchronization. The terminal may identify the second carrier that isout of synchronization. The terminal may identify at least one carrierthat is out of synchronization from among a plurality of carriers whendetermining the success or failure of synchronization of each carrier inoperation 601. At least one carrier that is out of synchronizationincludes the second carrier.

The terminal may perform synchronization compensation based on the firstsynchronization in order to determine the second synchronization. Thesynchronization compensation includes an operation of determiningcompensated synchronization to be applied as the second synchronization.As described above, the terminal identifies at least one carrier that isin synchronization for the synchronization compensation. At least onecarrier that is in synchronization includes the first carrier.

According to various embodiments, the terminal may performsynchronization compensation based on the synchronization of the atleast one carrier in synchronization. That is, the terminal may performsynchronization compensation using all the carriers that are insynchronization. Alternatively, according to various embodiments, theterminal may perform synchronization compensation based on thesynchronization of some of one or more carriers that are insynchronization. That is, the terminal may perform synchronizationcompensation using some carriers (hereinafter, referred to as“compensation carriers”) suitable for the synchronization compensation,among the carriers that are in synchronization, instead of using all thecarriers in synchronization.

The terminal may perform synchronization compensation based on thesynchronization of the compensation carrier. The terminal may identify acompensation carrier, among one or more carriers that are insynchronization. The compensation carrier may include the first carrier.In some embodiments, the terminal may identify the first carrieraccording to a metric for at least one carrier that is insynchronization. For example, the terminal may identify the firstcarrier based on a gradient of synchronization, among one or morecarriers that are in synchronization. In some other embodiments, theterminal may identify the first carrier from among one or more carriersthat are in synchronization based on the second carrier that is out ofsynchronization. For example, the base station in the second cellproviding the second carrier may be associated with the first cell. Inaddition, for example, the second carrier may be adjacent to thefrequency band of the first cell. In addition, for example, the beam forthe second carrier may be the same as the beam for the first carrier.

The terminal may apply an average weight or individual weights to thesynchronization of one or more carriers in synchronization or one ormore compensation carriers, thereby performing synchronizationcompensation. The individual weights may be determined based on thefrequency characteristics, statistical characteristics, and physicalcharacteristics of the respective carriers. The terminal may determinethe second synchronization of the second carrier through thesynchronization compensation. For example, the terminal may average thesynchronization of three compensation carriers, thereby determining thecompensated synchronization. The terminal may determine the compensatedsynchronization as the second synchronization of the second carrier thatis out of synchronization. That is, the terminal may determine the celltime corresponding to the compensated synchronization as the cell timefor the second carrier.

In some embodiments, the at least one processor is further configured toapply an individual weight to the first synchronization.

In operation 605, the terminal may perform communication based on thesecond synchronization. The terminal may determine whether or not thesynchronization of the second carrier has been recovered based on thesecond synchronization. In other words, the terminal may determine thesuccess or failure of synchronization of the second carrier based on thesecond synchronization. For example, the terminal may determine thesuccess or failure of synchronization of the second cell providing thesecond carrier based on whether or not a synchronization signalcorrelation value is detected during the time corresponding to thesecond synchronization. In addition, the terminal may determine thesuccess or failure of synchronization of the second cell based on, forexample, whether or not the time corresponding to the secondsynchronization is within a predetermined range. In addition, theterminal may determine the success or failure of synchronization of thesecond cell based on, for example, the channel quality of a signalaccording to the second synchronization.

According to an embodiment, the condition for determining the success orfailure of synchronization in operation 605 may be the same as orsimilar to the condition for determining the success or failure ofsynchronization of each cell in operation 601. In addition, even thoughthe parameters for the determination condition are the same betweenoperation 601 and operation 605, threshold values for determiningwhether or not a specific condition is satisfied may be different.According to another embodiment, the condition for determining thesuccess or failure of synchronization in operation 605 may beindependent of the condition for determining the success or failure ofsynchronization of each cell in operation 601.

If the synchronization of the second carrier is successful, the terminalmay perform communication. If there are other carriers that are out ofsynchronization, in addition to the second carrier, the terminal maydetermine whether or not to recover the synchronization of the othercarriers that are out of synchronization. If the synchronization of allthe carriers set for the terminal is recovered, the terminal may performcommunication. If the synchronization of the second carrier fails, theterminal may re-establish the connection with the base station in orderto newly detect the synchronization for the second cell. For example,the terminal may perform the RRE. In addition, if the second cell is,for example, an Scell, the terminal may perform deletion and addition ofthe Scell.

According to various embodiments of the disclosure, when thesynchronization of a carrier, which is in synchronization, is changed,the compensated synchronization determined for a carrier, which is outof synchronization, may be changed as well. That is, as thesynchronization of the carrier in synchronization (e.g., the firstsynchronization in operation 601) is changed, a synchronizationdetermination value of the carrier performed with synchronizationcompensation (e.g., the second synchronization in operation 603) ischanged, thereby verifying whether or not the disclosure can beimplemented. According to some embodiments, the cell time of the carrier{e.g., primary component carrier (PCC)}, which is out ofsynchronization, may be changed to the cell time of the carrier {e.g.,secondary component carrier (SCC)}, which is in synchronization. Theimplementation of the disclosure may also be verified according to thedetection of the above change operation.

The synchronization compensation procedure has been described withreference to FIG. 6. Now, the operational flow of the terminal fordetermining the success or failure of synchronization of the carriersconstituting the CA according to the synchronization compensationprocedure of the disclosure will be described with reference to FIG. 7.

FIG. 7 illustrates a flowchart of a terminal for determining a successor failure of synchronization in the CA according to an embodiment ofthe disclosure. The terminal may be the terminal 120 in FIG. 1.

Referring to FIG. 7, the terminal may determine the success or failureof synchronization for each carrier in operation 701. The terminal maydetermine the success or failure of synchronization for each of thecarriers configured for the CA of the terminal. The determination on thesuccess or failure of synchronization may be performed independently foreach carrier. An example of detailed determination on the success orfailure of synchronization will be described with reference to FIGS. 8Aand 8B.

In operation 703, the terminal may determine whether or not there is acarrier that is out of synchronization. The terminal may determinewhether or not there is a carrier that is out of synchronization, amongthe carriers configured for the terminal, based on the result obtainedin operation 701. The terminal may perform operation 705 if there is atleast one carrier that is out of synchronization. On the other hand, ifthere is no carrier that is out of synchronization, the terminal mayperform operation 711.

In operation 705, the terminal may determine whether or not there is acarrier that is in synchronization. The terminal may determine whetheror not there is a carrier that is in synchronization, among the carriersconfigured for the terminal, based on the result obtained in operation701. If there is a carrier that is in synchronization, the terminal mayperform operation 707. On the other hand, if there is no carrier that isin synchronization (that is, if all of the carriers are out ofsynchronization), the terminal may perform operation 713. This is due tothe fact that if the synchronization of a carrier that is out ofsynchronization is compensated for using another carrier that is out ofsynchronization, the synchronization may further deteriorate.

In operation 707, the terminal may perform synchronization compensation.The terminal may identify at least one compensation carrier from one ormore carriers that are in synchronization. “Compensation carrier” refersto a carrier that provides the synchronization obtained forsynchronization compensation.

According to various embodiments, the terminal may identify at least onecompensation carrier based on a carrier that is out of synchronization.In some embodiments, the compensation carrier may be within a thresholdrange in the frequency domain of the carrier that is out ofsynchronization. That is, the compensation carrier may be a carrieradjacent to the carrier that is out of synchronization. The influence offrequency selectivity increases due to the increasing bandwidth. Sincethe synchronization may vary as the frequencies differ considerablybetween carriers, the terminal may determine the carrier adjacent to thecarrier, which is out of synchronization, to be the compensationcarrier.

In some embodiments, the compensation carrier may be associated with abeam of a carrier that is out of synchronization. For example, thecompensation carrier may be provided to the terminal via the same beamas that of the carrier that is out of synchronization. The beam may be aterminal beam. The terminal can increase the accuracy of thesynchronization compensation in the carriers corresponding to the samebeam information by applying synchronization information to each other.As another example, even if the compensation carrier is not the same asthe beam of the carrier that is out of synchronization, it may beprovided to another terminal via another beam in the same beam group.The beam group may be a set of beams having similar beam directions.This is due to the fact that the similarity between the synchronizationmay be relatively high because the paths of the transmitted signals aresimilar in the case of similar beam directions. Although the descriptionhas been made based on the beam of the terminal, the beam pair link orinformation on the beam of the base station may also be used todetermine the compensation carrier. For example, the terminal mayidentify, as a compensation carrier, the carrier provided by means ofthe same beam of the same base station as the carrier that is out ofsynchronization, among the carriers that are in synchronization.

In some embodiments, the compensation carrier may be associated with abase station providing a carrier that is out of synchronization. Thatis, the terminal may identify the compensation carrier in considerationof the physical arrangement of the cells. For example, the base stationproviding the compensation carrier may be the same as the base stationproviding a carrier that is out of synchronization. The terminal mayidentify the compensation carrier based on a timing advance group (TAG).As another example, the base station providing the compensation carriermay be located within a predetermined physical range from the basestation providing the carrier that is out of synchronization. Theterminal may identify the compensation carrier based on a TAG. This isdue to the fact that the similarity between the synchronization may beincreased if the physical locations of the base stations are the same orsimilar.

According to various embodiments, the terminal may identify at least onecompensation carrier according to the channel quality of each of one ormore carriers that are in synchronization. The channel quality may be atleast one of a signal-to-interference and noise ratio (SINR), acarrier-to-interference and noise ratio (CINR), a beam reference signalreceived power (BRSRP), a reference signal received power (RSRP), areference signal received quality (RSRQ), a received signal strengthindicator (RSRI), an error vector magnitude (EVM), a bit error rate(BER), and a block error rate (BLER). Hereinafter, the SINR will bedescribed as an example of the channel quality. In the disclosure, highchannel quality denotes the case where a channel quality value relatedto a signal magnitude is large or a channel quality value related to anerror rate is small. The higher the channel quality, the better thewireless communication environment that may be provided.

In some embodiments, the terminal may identify a carrier with highchannel quality as a compensation carrier. This is due to the fact thatthe higher the channel quality, the higher the reliability of thechannel. For example, the terminal may measure the RSRP of asynchronization signal of each of the carriers. The terminal mayidentify, as compensation carriers, the top N (N is an integer) carrierswith high RSRP of the synchronization signal, among the carriers thatare in synchronization.

In some other embodiments, the terminal may identify at least onecompensation carrier, among one or more carriers that are insynchronization, based on the degree of change in the synchronization.For example, the terminal may identify the carrier with the lowestdegree of change in synchronization as a compensation carrier. This isdue to the fact that the lowest degree of change means that thereliability of the obtained synchronization is high. As another example,if the amount of change in the synchronization of the carrier insynchronization alternates between negative numbers and positivenumbers, the terminal may not identify the corresponding carrier as acompensation carrier. This is due to the fact that even though thecarrier becomes synchronized, the reliability of the obtainedsynchronization may be low.

Although the conditions for identifying the compensation carrier havebeen described above, the disclosure is not limited thereto. Accordingto various embodiments, the terminal may identify at least onecompensation carrier by combining two or more of the above-describedconditions (e.g., frequency domain, beam, base station, channel quality,and the like).

The terminal may determine the synchronization of the carrier, which isout of synchronization, based on the synchronization of each of theidentified compensation carriers. For example, the terminal maydetermine the timing value (i.e., cell time) for the synchronization ofthe first carrier, which is the compensation carrier, as the timingvalue for the synchronization of the second carrier that is out ofsynchronization. The terminal may decode a signal of the second carrieraccording to the subframe boundary of the first carrier. As anotherexample, the terminal may determine the average value of thecompensation carriers as the synchronization of the second carrier thatis out of synchronization.

The terminal may determine the synchronization of the carrier that isout of synchronization, thereby performing synchronization compensation.If there are two or more carriers that are out of synchronization, theterminal may perform synchronization compensation for the respectivecarriers out of synchronization. In some embodiments, the terminal mayuse the carrier on which synchronization compensation is performed as acompensation carrier. The terminal may use the carrier on whichsynchronization compensation is performed as a compensation carrier toperform synchronization compensation for the carrier that is out ofsynchronization. In some other embodiments, the terminal may performsynchronization compensation for the respective carriers that are out ofsynchronization. Hereinafter, an example of detailed determination ofthe synchronization compensation will be described with reference toFIGS. 9 to 11B.

In operation 709, the terminal may determine whether or not all thecarriers have become synchronized. The terminal may determine whether ornot all the carriers constituting the CA of the terminal becomesynchronized. The terminal may skip the determination of the success orfailure of synchronization of the carrier that is in synchronization asa result of operation 701. The terminal may re-perform the determinationof the success or failure of synchronization of the carrier that is outof synchronization as a result of operation 701. The terminal maydetermine the success or failure of synchronization of the carrier thatis out of synchronization based on the synchronization determinedaccording to the synchronization compensation in operation 707. In otherwords, the terminal may determine whether or not to recover thesynchronization of the carrier that is out of synchronization accordingto the synchronization compensation in operation 707. The terminal mayperform operation 711 if all the carriers are in synchronization. On theother hand, if there is a carrier that is out of synchronization, theterminal may perform operation 713.

In operation 711, the terminal may determine the success ofsynchronization for the CA. The terminal may perform the CA. Theterminal may transmit or receive data via the configured carriers. Inoperation 713, the terminal may determine the failure of synchronizationfor the CA. In the case of the failure of synchronization for the CA, insome embodiments, the terminal may perform deletion/modification of theScell, or may perform a new reconnection procedure. In some otherembodiments, the terminal may re-perform the illustrated synchronizationcompensation procedure. In addition, in some other embodiments, theterminal may maintain a connection with the base station until thenumber of carriers that are out of synchronization exceeds a specifiedvalue. An example of the detailed determination of whether or not thesynchronization is recovered will be described with reference to FIG.12.

Although FIG. 7 illustrates that operations 703 to 705 are performedafter the success or failure of synchronization of each carrier isdetermined in operation 701, the disclosure is not limited thereto. Theterminal may perform operation 703 even if only one carrier that is outof synchronization is detected, or may perform operation 705 even ifonly one carrier that is in synchronization is detected.

FIG. 8A illustrates a flowchart of a terminal for determining thesuccess or failure of synchronization for each carrier according to anembodiment of the disclosure. The terminal may be the terminal 120 inFIG. 1. Hereinafter, the procedure for determining the success orfailure of synchronization for each carrier in FIG. 8A may be performedaccording to operation 701 in FIG. 7.

Referring to FIG. 8A, in operation 801, the terminal may determinewhether or not a maximum correlation value condition for the carrier issatisfied. The maximum correlation value condition means a condition fordetecting the success of synchronization of a carrier based on themaximum correlation value for a synchronization sequence.

Since the terminal does not know the time at which a synchronizationsignal is received, the terminal may perform a correlation operationevery unit time. The synchronization signal may include a sequence. Forexample, the synchronization signal may include a PSS sequence. Asanother example, the synchronization signal may include an SSS sequence.The terminal may perform a correlation operation based on a sequence fora synchronization signal (hereinafter, referred to as a “synchronizationsequence”). The terminal may calculate a plurality of correlation valuesthrough the correlation operation using the synchronization sequence.The terminal may determine a maximum correlation value, which is a peakamong a plurality of correlation values. The terminal may calculate themaximum correlation value exceeding a correlation threshold valuethrough the correlation operation in the unit time at which thesynchronization sequence is transmitted. This is due to the fact thatthe correlation operation is performed between the same synchronizationsequence so that a peak is derived from the correlation value. Theterminal may determine, as a synchronization time, the unit time havingthe maximum correlation value through the correlation operation.Meanwhile, if the synchronization fails, although the maximumcorrelation value is the largest one of the calculated correlationvalues, the maximum correlation value may be equal to or less than thecorrelation threshold value. The terminal may determine whether or notthe synchronization fails by comparing the maximum correlation valuewith the correlation threshold value. For example, the terminal maydetermine whether or not the maximum correlation value satisfies thefollowing equation.Corr_(max,m) >C _(t)  Equation 1

In Equation 1, “m” represents the index indicating a carrier.Corr_(max,m) may be the maximum correlation value of the carrier withindex m. C_(t) may be a correlation threshold value.

The terminal may determine the success or failure of synchronization ofa carrier based on whether or not the case where the maximum correlationvalue for the carrier does not exceed the correlation threshold value iscontinuously detected more than a threshold number of times. Thethreshold number of times may be preset to a fixed value (e.g., twice),or may be set to be variable depending on the channel state or the userinput. The terminal may determine whether or not the maximum correlationvalue condition is satisfied according to whether or not the case wherethe maximum correlation value for the carrier does not exceed thecorrelation threshold value is continuously detected a threshold numberof times or more.

The terminal may determine that the maximum correlation value conditionis satisfied if the number of times that the maximum correlation valuedoes not exceed the correlation threshold value successively is equal toor greater than a threshold number. The terminal may perform operation803. The terminal may determine that the maximum correlation valuecondition is not satisfied if the number of times that the maximumcorrelation value does not exceed the correlation threshold valuesuccessively is less than the threshold number. According to anembodiment, if the threshold number is 1, the terminal may determinethat the maximum correlation value condition is not satisfied inresponse to the detection indicating that the maximum correlation valuedoes not exceed the correlation threshold value. The terminal mayperform operation 809.

In operation 803, the terminal may determine whether or not asynchronization time condition for the carrier is satisfied. Thesynchronization time condition means a condition for detecting thesuccess of synchronization of a carrier based on the obtainedsynchronization of the carrier (i.e., cell time). The terminal maydetermine the cell time of the carrier as the synchronization of thecarrier. The terminal may determine whether or not the cell time iswithin a predetermined range. The cell time may be determined using thecell time offset (CTO) from a reference value. The terminal maydetermine whether or not the synchronization time condition is satisfieddepending on whether or not the cell time offset of the correspondingcarrier is within a specific range. For example, the terminal maydetermine whether or not the cell time offset of the first carriersatisfies the following equation.t _(s) ₁ <T _(CTO,m) <t _(s) ₂ Equation 2

In Equation 2, “m” represents the index indicating a carrier. T_(CTO,m)represents the cell time offset of the first carrier, and t_(s1) andt_(s2) represent the upper limit value and the lower limit value,respectively, of a specific range for the synchronization timecondition.

The terminal may determine that the synchronization time condition issatisfied if the cell time offset is within a certain range. Theterminal may perform operation 805. The terminal may determine that thesynchronization time condition is not satisfied if the cell time offsetis out of a specific range. This is due to the fact that the reliabilityof the synchronization of the corresponding carrier is lowered if thesynchronization obtained periodically (for example, at a period of 5 ms)is out of a certain range. The terminal may perform operation 809.

In operation 805, the terminal may determine whether or not the channelquality condition for the carrier is satisfied. The channel qualitycondition means a condition for detecting the success of synchronizationof the carrier based on the obtained channel quality of the carrier. Theterminal may determine whether or not the channel quality for thecarrier is higher than a predetermined reference (e.g., a referencevalue). For example, the terminal may determine whether or not the BLERof the physical downlink shared channel (PDSCH) satisfies the followingequation.BLER_(m) <R _(BLER)  Equation 3

In Equation 3, “m” represents the index indicating a carrier. BLER_(m)represents the BLER of the PDSCH for the carrier of index m. R_(BLER)represents a quality threshold value. The terminal may determine thatthe channel quality condition is satisfied if the BLER of the PDSCH isless than a threshold value.

The terminal may determine that the channel quality condition issatisfied if the channel quality is higher than a predeterminedreference. The terminal may perform operation 807. On the other hand, ifthe channel quality condition is lower than the predetermined reference,the terminal may perform operation 809.

In operation 807, the terminal may determine the success ofsynchronization of the carrier. In operation 809, the terminal maydetermine the failure of synchronization of the carrier. According tovarious embodiments, the terminal may perform operations 801 to 809 forthe respective carriers set for the CA of the terminal. The terminal mayseparately determine the success or failure of synchronization for eachcarrier.

A method for determining the success or failure of synchronization ofeach carrier has been described with reference to FIG. 8A. However, theserial connection of the three conditions shown in FIG. 8A is only anexample for determining the success or failure of synchronization, andthe disclosure is not limited thereto. In other words, the terminal maydetermine the success or failure of synchronization of the carrier invarious manners such as determining the success or failure ofsynchronization of the carrier with a different sequence of the threeconditions, determining the success or failure of synchronization of thecarrier with some conditions, or determining the success or failure ofsynchronization of the carrier by adding other conditions, which are notillustrated, to the above conditions. For example, if thesynchronization time condition of the carrier is satisfied, the terminalmay determine that the synchronization of the carrier is successfulwithout determining other conditions. As another example, if thesynchronization time condition of the carrier is satisfied, and if theBLER of the PDSCH of the carrier is less than a threshold value, theterminal may determine that the synchronization of the carrier issuccessful without determining the maximum correlation value condition.

The terminal determines the success or failure of synchronization ofeach carrier, thereby obtaining the synchronization of the carrier thatis in synchronization. The terminal may perform synchronizationcompensation before determining that a specific carrier is out ofsynchronization (hereinafter, referred to as “early synchronizationcompensation”). The early synchronization compensation is performedprior to the synchronization compensation performed after determiningthe success or failure of synchronization of each carrier, therebyreducing the compensation burden of the synchronization compensation andproviding quick synchronization recovery. That is, the terminal mayperform synchronization compensation prior to the synchronizationcompensation in operation 707 in FIG. 7. Hereinafter, an example ofearly synchronization compensation will be described with reference toFIG. 8B.

FIG. 8B illustrates a flowchart of a terminal for early synchronizationcompensation according to an embodiment of the disclosure. The terminalmay be the terminal 120 in FIG. 1. The terminal performs operation 801of the procedure for determining the success or failure ofsynchronization of each carrier shown in FIG. 8A.

Referring to FIG. 8B, the terminal may calculate a correlation value perunit time in operation 851. The terminal may calculate a correlationvalue for every unit time using a synchronization sequence.

In operation 853, the terminal may determine whether or not the maximumcorrelation value exceeds a correlation threshold value. The terminalmay identify the correlation value (i.e., the maximum correlation value)at which a peak occurs. The terminal may determine whether or not theidentified maximum correlation value exceeds a correlation thresholdvalue. The correlation threshold value may be a threshold value foridentifying a peak that occurs using a correlation operation of the sameor similar synchronization sequence. That is, if the maximum correlationvalue exceeds a correlation threshold value, the terminal may determinethat the synchronization for the carrier transmitting the correspondingsynchronization sequence is successful. The terminal may performoperation 865. On the other hand, if the maximum correlation value isequal to or less than the correlation threshold value, the terminal mayperform operation 855.

In operation 855, the terminal may determine whether or not thesynchronization compensation is available. The terminal may determinewhether or not there is a carrier for synchronization compensation. Thisis due to the fact that there is no input to perform synchronizationcompensation if there is no carrier that is in synchronization. Thus,the terminal may determine whether or not there is a carrier that is insynchronization. For example, the terminal may determine the carrierswhose maximum correlation value is equal to or more than the correlationthreshold value as a carrier in synchronization. The terminal mayidentify the indexes of the carriers satisfying Equation 1, among aplurality of carriers set for the terminal.

The maximum correlation value condition has been illustrated anddescribed as an example of a condition for determining the success orfailure of synchronization of each carrier in order to determine whetheror not the synchronization compensation is available. However, theterminal may also identify the carrier that is in synchronization usingother conditions (e.g., the synchronization time condition in FIG. 8A).If the synchronization compensation is unavailable, the terminal mayperform operation 865. If the synchronization compensation is available,the terminal may perform operation 857.

In operation 857, the terminal may perform synchronization compensation.The terminal may perform early synchronization compensation. The earlysynchronization compensation, which is the same as or similar to thesynchronization compensation in operation 707 in FIG. 7, means aprocedure for obtaining the synchronization of a carrier out ofsynchronization based on the synchronization of the carrier that is insynchronization.

The terminal may determine a compensation value (e.g., Atm, where “m” isthe index of a carrier out of synchronization) based on thesynchronization of at least one of the carriers that are insynchronization, which are identified in operation 855. The compensationvalue means a value for compensating for a carrier that is out ofsynchronization. For example, the compensation value may be determinedbased on an average of synchronization of one or more carriers insynchronization. As another example, the compensation value may bedetermined based on the synchronization of one of one or more carriersin synchronization. The terminal may apply the compensation value to thecell time of the carrier out of synchronization. For example, if thecell time offset of the previous frame of the carrier out ofsynchronization is t_(offset), the terminal may determine the cell timeoffset in the current frame to be t_(offset)+Δt_(m).

In operation 859, the terminal may determine whether or not thesynchronization compensation is successful. The terminal may determinewhether or not the synchronization-compensated cell time offset iswithin a specific range. For example, the terminal may determine whetheror not the synchronization-compensated cell time offset satisfies thefollowing equation.t _(e) ₁ <t _(offset) +Δt _(m) <t _(e) ₂   Equation 4

In Equation 4, t_(offset) represents a cell time offset in the previousframe, and Δt_(m) represents a compensation value for a carrier of anindex m. t_(s1) and t_(s2) represent the upper limit value and the lowerlimit value, respectively, of a range for early synchronizationcompensation.

Although the synchronization time condition has been illustrated anddescribed as an example of a condition for determining the success orfailure of the synchronization compensation, it is available to identifythe carrier that is in synchronization using other conditions (e.g., thechannel quality condition in FIG. 8A). The terminal may performoperation 865 if the synchronization compensation is successful. Theterminal may perform operation 861 if the synchronization compensationfails.

In operation 861, the terminal may determine whether or not the numberof times the maximum correlation value is less than the correlationthreshold value exceeds a threshold number. Operation 861 corresponds tooperation 801 in FIG. 8A, and thus a description of the same or similaroperations will be omitted. The terminal may perform operation 863 ifthe number of times the maximum correlation value is less than thecorrelation threshold value exceeds the threshold number. On the otherhand, if the number of times the maximum correlation value is less thanthe correlation threshold value is equal to or less than the thresholdnumber, the terminal may perform operation 865.

In operation 863, the terminal may determine that the maximumcorrelation value condition is not satisfied. The terminal may determinethat the carrier has failed in synchronization. In operation 865, theterminal may determine that the maximum correlation value condition issatisfied. The terminal may determine that the synchronization of thecorresponding carrier is successful, or may determine the success orfailure of synchronization of the carrier by further determining whetheror not other conditions are satisfied.

Although an example of performing early synchronization compensationwhile determining whether or not the maximum correlation value conditionis satisfied has been described in FIG. 8B, the early synchronizationcompensation of the disclosure may be performed even during thedetermination of other conditions. For example, the terminal may performearly synchronization compensation when determining whether or not thesynchronization time condition is satisfied according to operation 803in FIG. 8A. In addition, according to an embodiment, the terminal mayperform the early synchronization compensation multiple times, insteadof performing the same once, under particular conditions.

An example of determining the success or failure of synchronization ofeach carrier has been described with reference to FIGS. 8A and 8B.Hereinafter, operations and embodiments of a terminal for compensatingfor synchronization of a carrier, which is out of synchronization, willbe described with reference to FIGS. 9 to 11B.

FIG. 9 illustrates a flowchart of a terminal for synchronizationcompensation according to an embodiment of the disclosure. The terminalmay be the terminal 120 in FIG. 1. FIG. 9 illustrates operation 707 inFIG. 7.

Referring to FIG. 9, the terminal may obtain a first offset of a carrierthat is in synchronization in operation 901. The offset, which is a celltime offset, is a value indicating how much the cell timer for thecorresponding carrier is shifted from a reference timer (e.g., FRC). Therespective carriers set for the terminal may share a reference timer.The reference timer provides a reference value, which is commonlyapplied to the respective carriers. The value of the cell timer for eachcarrier may indicate the actual cell time through an offset from thereference value. The first offset may be the offset for the cell time ofthe first carrier, which is at least one compensation carrier, among oneor more carriers that are in synchronization.

According to various embodiments, the carrier of the first offset may bea carrier using the same beam direction as that of the carrier that isout of synchronization. The terminal may identify, as the first offset,the offset of the carrier that is in synchronization, which uses thesame beam as that of the carrier that is out of synchronization.

According to various embodiments, the carrier of the first offset may bewithin a predetermined range of the carrier that is out ofsynchronization in the frequency band. That is, the carrier of the firstoffset may be adjacent to the carrier that is out of synchronization inthe frequency band. The influence of the frequency selectivity may bereduced by compensating for the synchronization of the carrier that isout of synchronization using the synchronization of the adjacent carrierin the frequency band.

According to various embodiments, the carrier of the first offset may bea carrier with high (excellent) channel quality, among the carriers thatare in synchronization. For example, the carrier of the first offset maybe the carrier having the smallest change in the variation value of thecell timing, among the carriers that are in synchronization. Inaddition, the carrier of the first offset may be, for example, thecarrier with the highest RSRQ, among the carriers that are insynchronization. It is available to perform synchronization compensationwith high reliability by compensating for the synchronization of thecarrier that is out of synchronization using the synchronization of thecarrier with high channel quality.

In operation 903, the terminal may determine a second offset of thecarrier that is out of synchronization based on the first offset.According to various embodiments, the terminal may determine a secondoffset of the carrier that is out of synchronization using the firstoffset. For example, the terminal may apply the value of the firstoffset to the second offset of the carrier that is out ofsynchronization. That is, the second offset may be equal to the firstoffset. As another example, the terminal may determine the second offsetby adding the compensation value between the carrier of the first offsetand the carrier of the second offset to the first offset.

According to various embodiments, the terminal may use the offset valuesof the compensation carriers, including the first offset, therebydetermining the offset of the second carrier that is out ofsynchronization. In some embodiments, the terminal may determine thesecond offset using an average of the offset values. In some otherembodiments, the terminal may apply respective weights to the offsetvalues, thereby determining the second offset. For example, the terminalmay apply the weights differently depending on how close the respectivecompensation carriers are to the carrier that is out of synchronizationin the frequency domain, thereby determining the second offset. Asanother example, the terminal may apply the weights differentlydepending on the channel quality of each of the compensation carriers,thereby determining the second offset. As another example, the terminalmay apply the weights differently depending on the geographicalproximity of the respective compensation carriers to the cell providingthe carrier that is out of synchronization, thereby determining thesecond offset. The geographical proximity may be determined based on atleast one of TA, beam information, geographical information such as thatfrom a global positioning system (GPS), a cell identifier (ID), andstatistical information.

FIG. 10 illustrates an example of a timer of a terminal forsynchronization compensation according to an embodiment of thedisclosure. The terminal may be the terminal 120 in FIG. 1.

Referring to FIG. 10, the terminal may include a reference timer 1010.The reference timer 1010 is intended to provide a common reference tothe respective carriers for the terminal, and the respective cell timersmay be configured to refer to the value of the reference timer 1010.FIG. 10 illustrates an FRC as a reference timer. That is, the FRC may beconfigured to provide a common reference value to the carriers for theterminal. The terminal may drive the FRC whenever it is turned on. Theterminal may determine the synchronization time of the base stationbased on the FRC. The terminal may continuously increase the FRC valueaccording to the number of samples. In general, the FRC may beconfigured in the form of at least one of “number of frames”, “number ofsubframes”, “number of slots”, or “number of samples”.

The value indicated by the indicator 1015 may be an FRC value. Theindicator 1015 of the FRC circulates in a specified period until theterminal is turned off. In some embodiments, the specified period may be10 milliseconds (ms). The terminal may repeatedly circulate theindicator 1015 every 10 ms. The indicator 1015 may repeatedly indicatean FRC value in a specified period.

The terminal may include a cell timer. The terminal may include celltimers for carriers configurable for the terminal. For example, theterminal may include a first cell timer 1021 for the first carrier and asecond cell timer 1022 for the second carrier. The first cell timer 1021may include a first cell time indicator 1041. The first cell timeindicator 1041 may indicate the cell time K₁ of the first cell for thefirst carrier. The second cell timer 1022 may include a second cell timeindicator 1042. The second cell time indicator 1042 may indicate thecell time K₂ of the second cell for the second carrier. The cell timermay repeatedly indicate the cell time every specified period. Thespecified period may be set to be equal to the specified period of theFRC. In other words, the cell timer may have a value of the same periodas that of the FRC, with only a starting point different therefrom.

A CTO may be defined as a value relative to the FRC calculated throughthe synchronization signal search of the base station. The first celltime indicator 1041 may indicate the state shifted by a first CTO 1031from the value of the FRC. That is, the first cell time indicator 1041may indicate the position shifted by the first CTO 1031 from theindicator 1015. The second cell time indicator 1042 may indicate thestate shifted by a second CTO 1032 from the value of the FRC. That is,the second cell time indicator 1042 may indicate the position shifted bythe second CTO 1032 from the indicator 1015. The terminal may determinethe actual synchronization time based on the FRC value and the CTOvalue. The value obtained by adding the CTO value of the cell to the FRCvalue may mean the actual synchronization time of the correspondingcell.

A synchronization time condition may be used to determine the success orfailure of synchronization of the cell. That is, the terminal maydetermine the success or failure of synchronization of the cellaccording to whether or not the cell time of the cell is within theexpected synchronization range {i.e., an effective range (e.g., Equation2)}.

The effective range for the first carrier may be a first effective range1051. The terminal may obtain the synchronization of the first carrierfrom the synchronization signal of the first cell. The terminal maydetermine the cell time of the first carrier based on the first CTO1031. The terminal may determine the cell time of the first carrieraccording to the value indicated by the first cell time indicator 1041.Since the cell time K₁ indicated by the first cell time indicator 1041is within the first effective range 1051, the terminal may determinethat the synchronization of the first cell is successful.

The effective range for the second carrier may be a second effectiverange 1052. The terminal may obtain the synchronization of the secondcarrier from a synchronization signal of the second cell. The terminalmay determine the cell time of the second carrier based on the secondCTO 1032. The terminal may determine the cell time of the second carrieraccording to the value indicated by the second cell time indicator 1042.Since the cell time K₂ indicated by the second cell time indicator 1042is out of the second effective range 1052, the terminal may determinethat the synchronization of the second cell has failed.

Since the second carrier has failed in synchronization, the terminal maybe required to recover the synchronization of the second carrier. Theterminal may determine the synchronization of the second carrier, whichis out of synchronization, based on the synchronization of the firstcarrier, which is in synchronization.

In some embodiments, the first carrier and the second carrier may betransmitted from the same base station to the terminal, and the terminalmay be served through the first carrier and the second carrier using thesame beam. Therefore, the synchronization of the first carrier and thesynchronization of the second carrier may be set to be equal or similarwithin a predetermined error range.

If the second carrier is out of synchronization, the terminal maydetermine the synchronization of the first carrier as thesynchronization of the second carrier. More specifically, the terminalmay determine the first CTO 1031 as a compensation CTO 1062. Theterminal may compensate for the synchronization of the second carrieraccording to the FRC value and the compensation CTO value. The terminalmay move the second cell time indicator 1042 so as to point to theposition shifted by the compensation CTO 1062 from the indicator 1015.The terminal may determine that the synchronization of the secondcarrier has been recovered as the cell time K₂ indicated by the secondcell time indicator 1024 is within the second effective range 1052. Theterminal may determine that the synchronization of the second carrier issuccessful.

According to various embodiments, the terminal may include an FRC asshown in FIG. 10. In some embodiments, the terminal may include separatehardware in which the FRC is implemented. The respective cell timers inthe terminal may be operatively connected to the FRC. As the FRC isimplemented as independent hardware, it is available to reduce an errordue to external influences and to provide accurate synchronization. Insome other embodiments, the terminal may include a memory in which theFRC is implemented as software. The respective cell timers in theterminal may be implemented so as to refer to the memory.

The terminal may include a single FRC, and each cell timer may performsynchronization by referring to the single FRC. As the FRC is shared bythe respective cell timers, the value of the FRC may be used as areference for obtaining the synchronization of each cell timer.Meanwhile, the disclosure does not exclude a configuration in which theterminal includes a plurality of FRCs, as well as a single FRC. Eachcell timer may be implemented so as to refer to some of a plurality ofFRCs. Even if a plurality of FRCs are implemented, it may be requiredthat the same FRC value be provided to the respective cell timers inorder to provide a reference value.

FIG. 11A illustrates an example of synchronization compensation based oncell-deployment according to an embodiment of the disclosure. Thecell-deployment may include a physical location where each cell isprovided, coverage, the frequency band of the cell, and so on. Inaddition, the cell-deployment may include base station deployment.

Referring to FIG. 11A, a terminal 1120 may be served by a first basestation 1101 through a first carrier 1121. The terminal 1120 may beserved by a second base station 1102 through a second carrier 1122. Theterminal 1120 may be served by a third base station 1103 through a thirdcarrier 1123. The terminal 1120 may be serviced by a fourth base station1104 through a fourth carrier 1124. The terminal 120 may perform the CAincluding four carriers. Hereinafter, an example in which the first basestation 1101, the second base station 1102, and the third base station1103 are spaced a long distance apart from each other and the third basestation 1103 and the fourth base station 1104 are spatially adjacent toeach other will be described.

If the physical locations of the base stations are spaced quite a longdistance apart from each other, there may be a difference in thepropagation path between the synchronization signals transmitted fromthe base stations, so that the difference in the synchronization betweenthe carriers of the adjacent frequency bands may increase. If thesimilarity between the synchronization is not satisfied as describedabove, it may be difficult to use the respective pieces ofsynchronization mutually for synchronization compensation. For example,even if the first carrier 1121 is in synchronization and the secondcarrier 1122 is out of synchronization, the terminal 1120 may notcompensate for the synchronization of the second carrier 1122 based onthe synchronization of the first carrier 1121.

Meanwhile, if the positions of the respective base stations are the sameor adjacent to each other, the propagation paths of the synchronizationsignals transmitted from the respective base stations may be similareven if the base stations are different. Accordingly, thesynchronization between the base stations may be similar. If thesimilarity between the synchronization is satisfied, the respectivepieces of synchronization may be used mutually for synchronizationcompensation. For example, if the third carrier 1123 is insynchronization and the fourth carrier 1124 is out of synchronization,the terminal 1120 may compensate for the synchronization of the fourthcarrier 1124 based on the synchronization of the third carrier 1123. Forexample, the terminal may apply the cell time of the third carrier 1123to the cell time of the fourth carrier 1124. As described above, inorder to determine the synchronization of another carrier based on thesynchronization of a specific carrier, the terminal is required toconsider cell-deployment. Hereinafter, when the similarity between thesynchronization is satisfied, it will be expressed that the cells areco-located with each other for the convenience of description.

In some embodiments, the terminal may perform synchronizationcompensation based on the TA. The terminal may calculate the degree ofcorrespondence of physical location between the terminal and each basestation according to a TA value received from the base station. Theterminal may use the mutually-obtained synchronization forsynchronization compensation in the case of base stations in which thedifference between the TA values is less than a threshold range. Inaddition, a timing advance group (TAG) may be used in a manner similarto the TA. For example, the terminal may perform synchronizationcompensation for the cells provided from the base station in the sameTAG using inter-cell synchronization. That is, the cells provided fromthe base station in the same TAG are co-located with each other.

In addition, in some embodiments, the terminal may performsynchronization compensation based on statistical information. The basestations located adjacent to each other may have the same statisticalcharacteristics. The statistical characteristics may include propagationdelay, Doppler shift, delay spread, frequency of terminal access, andfrequency of beam use. The terminal may determine base stations havingcorrelation between statistical characteristics higher than a thresholdvalue to be the same group, and may perform synchronization compensationusing the synchronization between the base stations in the same group.That is, the cells provided from the respective base stations in thesame group are co-located with each other.

In addition, in some embodiments, the terminal may performsynchronization compensation based on beam information. When receiving asynchronization signal by means of the same terminal beam, the terminalmay perform synchronization compensation using the synchronization ofthe cell associated with the same terminal beam. When receiving asynchronization signal from the beam of the same base station, theterminal may perform synchronization compensation using thesynchronization of the cell associated with the beam of the same basestation. When receiving a synchronization signal using the same beampair, the terminal may perform synchronization compensation using thesynchronization of the cell associated with the same beam pair. On theother hand, apart from the same beam or the same beam pair, the terminalmay manage the beam group according to the directions of the beams,thereby performing synchronization compensation more effectively. Thecells provided through respective beams in the beam group are co-locatedwith each other.

The terminal may include a plurality of RF paths in order to perform theCA. The terminal may support the CA over many carriers through aplurality of RF paths. In this case, a used beam and an available bandmay be determined according to the RF because of hardware constraints.Hereinafter, an example of performing synchronization compensation basedon the RF path will be described with reference to FIG. 11B.

FIG. 11B illustrates an example of synchronization compensation based onthe RF path according to an embodiment of the disclosure. Each RF chainmay form an independent radio path. The radio path may include an RFmodule and a modem. The terminal may include a plurality of radiofrequency (RF) chains for the CA. The terminal cannot flexibly supportall bands for the CA by means of a single RF chain due to the physicalconstraints of the filter. Thus, each RF chain may be configured toprovide at least one specific carrier depending on the configuration ofthe filter. According to various embodiments, the terminal may utilizeinformation on the beam formed by each RF chain in order to obtainsynchronization information for each carrier. Hereinafter, the casewhere a first RF chain provides a first beam 1171, a second RF chainprovides a second beam 1172, and a third RF chain provides a third beam1173 will be described as an example.

Referring to FIG. 11B, the terminal 1170 may perform communication witha first base station 1151. The first beam 1171 of the terminal mayestablish a radio link with a first beam 1161 of the first base station1151. The terminal 1170 may perform communication with a second basestation 1152. The second beam 1172 of the terminal may establish a radiolink with a second beam 1162 of the second base station 1152. Theterminal 1170 may perform communication with a third base station 1153.The third beam 1173 of the terminal may establish a radio link with athird beam 1163 of the third base station 1153. The terminal maycommunicate with each of three base stations, which are physicallyseparated, via three beams of the terminal. The first beam 1171, thesecond beam 1172, and the third beam 1173 of the terminal may be beamsthat are oriented in respective directions. The directions may bespatially separated from each other. As the respective beams areoriented in spatially directions that are spatially separated, thesynchronization signals received via the respective beams are receivedvia different RF paths as well.

According to various embodiments, the terminal may performsynchronization compensation between carriers supported by a single RFchain. For example, in the case where the first RF chain can provide thefirst carrier and the second carrier, if the first carrier is out ofsynchronization, the terminal may perform synchronization compensationusing the synchronization of the second carrier, thereby determining thesynchronization of the first carrier.

According to various embodiments, the terminal may not identify thecarrier supported through another RF chain as a compensation carrier.That is, if the terminal identifies a compensation carrier, among thecarriers that are in synchronization, the terminal may not identify, asa compensation carrier, a carrier provided from the RF chain that isdifferent from the carrier that is out of synchronization.

As described with reference to FIG. 11B, the terminal may identify thecompensation carrier for synchronization compensation based on beaminformation and synchronization information identified according to thephysical hardware structure.

FIG. 12 illustrates a flowchart of a terminal for determining a successor failure of the CA synchronization according to an embodiment of thedisclosure. The terminal may be the terminal 120 in FIG. 1.

Referring to FIG. 12, the terminal may identify a carrier in operation1201. The terminal may identify the carriers set for the CA of theterminal in sequence.

In operation 1203, the terminal may determine the success or failure ofsynchronization of the carrier identified in operation 1201. Theterminal may determine whether or not a channel quality condition forthe identified carrier is satisfied. The channel quality condition maybe intended to determine the success or failure of synchronization basedon the channel quality. The terminal may determine whether or not thechannel quality of the carrier is higher than a predetermined reference.If the channel quality is higher than the predetermined reference, theterminal may determine that the condition is satisfied. For example, theterminal may determine whether or not the BLER of the PDSCH of thecarrier is a quality threshold value (R_(BLER2)). The quality thresholdvalue may be set to be equal to or different from the quality thresholdvalue in operation 805 in FIG. 8A. If the BLER is equal to or greaterthan the quality threshold value, the terminal may determine that thechannel quality condition is satisfied. If the channel quality conditionis satisfied, the terminal may perform operation 1205. If the channelquality condition is not satisfied, the terminal may perform operation1209.

In operation 1205, the terminal may determine whether or not the successor failure of synchronization has been determined for all the carriers.That is, the terminal may determine whether or not the determination ofwhether or not the channel quality condition is satisfied in operation1203 has been performed for all of the carriers. This is due to the factthat the terminal can transmit and receive data through the CA withoutunnecessary decoding or processing delay only if all the carriers are insynchronization. The terminal may determine whether or not the carrier,which has determined the channel quality condition in operation 1203 ofthe current cycle, is the last of the carriers set for the terminal.

If the success or failure of synchronization has been determined for allthe carriers, the terminal may perform operation 1207. If the success orfailure of synchronization has not been determined for all the carriers,the terminal may re-perform operation 1201. The terminal may identifythe carrier (e.g., the carrier of index m+1) subsequent to the carrier(e.g., the carrier of index m) identified in the previous cycle inoperation 1201. The terminal may repeat operations 1201 to 1205 todetermine the success or failure of synchronization for all thecarriers.

In operation 1207, the terminal may determine that the CAsynchronization is successful. The terminal may perform the CA. Inoperation 1209, the terminal may determine that the CA synchronizationhas failed. The terminal cannot perform the CA according to thecurrently configured carriers. The terminal may perform additionalprocedures to recover the synchronization of the carrier that is out ofsynchronization. For example, the terminal may perform an RRE procedureto reconnect to the base station.

Although the channel quality condition has been described by way of anexample in FIG. 12, the disclosure is not limited thereto. The terminalmay also determine the success or failure of the CA synchronizationusing other conditions or additional conditions. For example, theterminal may determine the success or failure of the CA synchronizationbased on the synchronization time condition (i.e., whether or not thesynchronization of each of the compensated carriers is within apredetermined range).

FIG. 13 illustrates a flowchart of a terminal for signal processingaccording to the success or failure of CA synchronization according toan embodiment of the disclosure. The terminal may be the terminal 120 inFIG. 1. FIG. 13 illustrates a procedure of the terminal following theprocedure in FIG. 7 or 12.

Referring to FIG. 13, the terminal may determine the success or failureof the CA synchronization in operation 1301. The terminal may determinethe success or failure of the CA synchronization as shown in FIG. 12. Ifthe CA synchronization is successful, the terminal may perform operation1303. If the CA synchronization fails, the terminal may performoperation 1305.

In operation 1303, the terminal may process baseband signals. Theterminal may process baseband signals received from the respective cellsconstituting the CA in order to perform the CA. For example, theterminal may decode the Pcell signal and the Scell signal, respectively.

In operation 1305, the terminal may determine radio link failure (RLF).The terminal may declare the RLF, and may search for synchronization ofthe Pcell again. In addition, the terminal may perform the RRE. That is,the terminal may release all of the settings and resource allocationmaintained during the connection, and may re-perform the initialconnection procedure and the setting procedure related thereto. Theterminal may also reset and reactivate the Scell. Although thedisclosure describes a synchronization recovery procedure forcompensating for the synchronization of a carrier that is out ofsynchronization using the synchronization of a carrier that is insynchronization, a reconnection procedure (e.g., RRE) performed by theterminal after determining whether or not the synchronization isrecovered by performing the synchronization compensation, as well as thesynchronization recovery, may also be understood as an embodiment.

Although FIG. 13 illustrates that the terminal declares the RLF if theCA synchronization fails, the terminal may not immediately declare theRLF. In some embodiments, if the cells that are out of synchronizationare Scells, the terminal may determine whether or not to maintain the CAor whether or not to declare the RLF based on the number of Scells thatare out of synchronization. In some other embodiments, if the cells thatare out of synchronization are Scells, the terminal may add, to theScells, a carrier that is configured for the CA after excluding theScells but is not activated for the Scells. The terminal may add theScell for the CA using the synchronization information obtained duringthe inter-frequency measurement.

Examples for obtaining and compensating for the synchronization of eachof the carriers set for the CA have been described in the disclosure.However, the disclosure is not limited to the CA. All procedures forrecovering synchronization of the frequency of a carrier that is out ofsynchronization, using a synchronization signal transmitted throughanother carrier frequency may be understood as an embodiment of thedisclosure. For example, the terminal may recover synchronization of aspecific carrier frequency (e.g., NR cell) using the synchronization ofanother carrier frequency (e.g., LTE cell) in a dual-connectivitysituation.

According to various embodiments, the terminal may performsynchronization compensation of the disclosure when performinginter-frequency measurement. For example, the terminal may perform firstmeasurement for the f₁ frequency band and second measurement for the f₂frequency band. It is assumed that both the f₁ frequency band and the f₂frequency band are located in the same base station or are locatedphysically adjacent to each other, thereby satisfying thesynchronization similarity. In this case, if the synchronization for thefirst measurement fails, the terminal may determine the synchronizationof the first frequency band obtained in the first measurement based onthe synchronization of the f₂ frequency band obtained in the secondmeasurement. As another example, the terminal may performsynchronization compensation based on the synchronization of each of theneighboring cells obtained through the inter-frequency measurement, evenif communication is performed using a single carrier. As anotherexample, the terminal may perform synchronization compensation for thecarrier configured and activated for the CA based on the synchronizationof a carrier that is configured for the CA but is not activated.

Although the disclosure describes the PSS or SSS in the cellular band asan example of a synchronization signal, all signals for obtainingsynchronization may be understood as an embodiment of the disclosure.For example, if the Scell is operating in the unlicensed band for LAAsupport, a discovery signal may be used to obtain synchronization of thecell.

In the disclosure, although the expression “equal to or more than” or“equal to or less than” has been used in order to determine whether ornot a specific condition is satisfied or fulfilled, this is only anexample and does not exclude the expression “more than” or “less than”.The expression “equal to or more than” can be replaced with “more than”,the expression “equal to or less than” can be replaced with “less than”,and the expression “equal to or more than and less than” can be replacedwith “more than and equal to or less than” in the conditions above.

Methods according to embodiments stated in claims and/or specificationsof the disclosure may be implemented in hardware, software, or acombination of hardware and software.

When the methods are implemented by software, a computer-readablestorage medium for storing one or more programs (software modules) maybe provided. The one or more programs stored in the computer-readablestorage medium may be configured for execution by one or more processorswithin the electronic device. The at least one program may includeinstructions that cause the electronic device to perform the methodsaccording to various embodiments of the disclosure as defined by theappended claims and/or disclosed herein.

The programs (software modules or software) may be stored innon-volatile memories including a random access memory and a flashmemory, a read only memory (ROM), an electrically erasable programmableread only memory (EEPROM), a magnetic disc storage device, a compactdisc-ROM (CD-ROM), digital versatile discs (DVDs), or other type opticalstorage devices, or a magnetic cassette. Alternatively, any combinationof some or all of the may form a memory in which the program is stored.Further, a plurality of such memories may be included in the electronicdevice.

In addition, the programs may be stored in an attachable storage devicewhich is accessible through communication networks such as the Internet,Intranet, local area network (LAN), wide area network (WAN), and storagearea network (SAN), or a combination thereof. Such a storage device mayaccess the electronic device via an external port. Further, a separatestorage device on the communication network may access a portableelectronic device.

In the above-described detailed embodiments of the disclosure, acomponent included in the disclosure is expressed in the singular or theplural according to a presented detailed embodiment. However, thesingular form or plural form is selected for convenience of descriptionsuitable for the presented situation, and various embodiments of thedisclosure are not limited to a single element or multiple elementsthereof. Further, either multiple elements expressed in the descriptionmay be configured into a single element or a single element in thedescription may be configured into multiple elements.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: based on detecting that asecond cell is out of synchronization, identifying a first cell that isin synchronization; obtaining second synchronization information of thesecond cell based on first synchronization information of the identifiedfirst cell; and performing a communication based on the secondsynchronization information, wherein the first cell is different fromthe second cell.
 2. The method of claim 1, further comprising:determining whether each of a plurality of cells for the terminal is insynchronization to identify whether the second cell is out ofsynchronization or not, wherein the plurality of cells includes thefirst cell and the second cell.
 3. The method of claim 2, wherein thedetermining of whether each of the plurality of cells is insynchronization comprises: determining whether each of the plurality ofcells is in synchronization based on at least one of: whether a maximumcorrelation value of each of the plurality of cells according to asynchronization sequence exceeds a correlation threshold value, whethera cell time of each of the plurality of cells is within a predeterminedrange, or whether a channel quality of each of the plurality of cells isequal to or more than a threshold value.
 4. The method of claim 1,wherein the second synchronization information of the second cell isobtained based on information on at least one beam used for the firstcell and information on at least one beam used for the second cell. 5.The method of claim 1, wherein a cell time offset according to thesecond synchronization information of the second cell is determined tocorrespond to a cell time offset of the first synchronizationinformation of the first cell, and wherein the first cell and the secondcell are associated with a same beam of the terminal.
 6. The method ofclaim 1, wherein a cell time offset according to the secondsynchronization information of the second cell is determined tocorrespond to a cell time offset of the first synchronizationinformation of the first cell, and wherein the first cell and the secondcell are associated with a same beam of a base station providing thefirst cell and the second cell.
 7. The method of claim 1, wherein theperforming of the communication comprises: determining whether thesecond cell is in synchronization or not based on the secondsynchronization information; and performing the communication accordingto a carrier aggregation (CA) for the first cell and the second cell ifthe second cell is in synchronization, and performing the communicationusing the first cell without the second cell if the second cell is outof synchronization.
 8. The method of claim 7, wherein the performing ofthe communication comprises: performing a secondary cell (S Cell)deletion of the second cell if the second cell is out ofsynchronization.
 9. A terminal in a wireless communication system,comprising: at least one transceiver; and at least one processorconfigured to be operatively connected to the at least one transceiver,wherein the at least one processor is further configured to: identify afirst cell that is in synchronization based on detecting that a secondcell is out of synchronization, obtain second synchronizationinformation of the second cell based on first synchronizationinformation of the identified first cell, and perform a communicationbased on the second synchronization information, wherein the first cellis different from the second cell.
 10. The terminal of claim 9, whereinthe at least one processor is further configured to determine whethereach of a plurality of cells for the terminal is in synchronization toidentify whether the second cell is out of synchronization or not. 11.The terminal of claim 10, wherein, to determine whether each of theplurality of cells is in synchronization, the at least one processor isconfigured to determine whether each of the plurality of cells is insynchronization based on at least one of: whether a maximum correlationvalue of each of the plurality of cells according to a synchronizationsequence exceeds a correlation threshold value, whether a cell time ofeach of the plurality of cells is within a predetermined range, orwhether a channel quality of each of the plurality of cells is equal toor more than a threshold value.
 12. The terminal of claim 9, wherein thesecond synchronization information of the second cell is obtained basedon information on at least one beam used for the first cell andinformation on at least one beam used for the second cell.
 13. Theterminal of claim 9, wherein a cell time offset according to the secondsynchronization information of the second cell is determined tocorrespond to a cell time offset of the first synchronizationinformation of the first cell, and wherein the first cell and the secondcell are associated with a same beam of the terminal.
 14. The terminalof claim 9, wherein a cell time offset according to the secondsynchronization information of the second cell is determined tocorrespond to a cell time offset of the first synchronizationinformation of the first cell, and wherein the first cell and the secondcell are associated with a same beam of a base station providing thefirst cell and the second cell.
 15. The terminal of claim 9, wherein, inorder to perform the communication, the at least one processor isconfigured to: determine whether the second cell is in synchronizationor not based on the second synchronization information, perform thecommunication according to a carrier aggregation (CA) for the first celland the second cell if the second cell is in synchronization, andperform the communication using the first cell without the second cellif the second cell is out of synchronization.
 16. The terminal of claim15, wherein, in order to perform the communication, the at least oneprocessor is further configured to: perform a secondary cell (SCell)deletion of the second cell if the second cell is out ofsynchronization.
 17. The method of claim 1, wherein the first cell andthe second cell are associated with a same serving beam of a basestation.
 18. The method of claim 1, wherein the performing of thecommunication comprises changing a synchronization parameter of thesecond cell from previous information to the second synchronizationinformation, and wherein the previous information is used when detectingthat the second cell is out of synchronization.
 19. The terminal ofclaim 9, wherein the first cell and the second cell are associated witha same serving beam of a base station.
 20. The terminal of claim 9,wherein, to perform the communication, the at least one processor isfurther configured to change a synchronization parameter of the secondcell from previous information to the second synchronizationinformation, and wherein the previous information is used when detectingthat the second cell is out of synchronization.
 21. The method of claim1, wherein the identifying of the first carrier that is insynchronization comprises: in response to detecting that the second cellis out of synchronization, identifying the first cell that is insynchronization.